This project was designed to investigate the incidence and etiology of transfusion-associated hepatitis in the newborn infant and to store sera for future testing when specific tests for non-A non-B agents become available. Transfused infants and non-transfused controls are followed with monthly blood testing for 5-6 months: Sera are routinely tested for alanine aminotransferase (ALT) levels and appropriate sera for serologic markers of hepatitis A, B, cytomegalovirus and Epstein-Barr virus infections. To date 10 of 208 (4.8%) transfused infants and only 1 of 47 (2.1%) controls developed hepatitis. None of the cases were symptomatic and none had evidence of HAV, HBV, or CMV infection.